Printed circuit wiring boards are conventionally made by etching and photographic processes using resist to define patterns in a conductive layer. If this resist breaks down or slight photographic or etching errors occur unwanted conductive patterns may appear between wanted conductive patterns. These may change circuit impedances such as capacitance and may cause arcing or short circuits between conductors. Intermittent types of short circuits are hard to locate with any conventional type of test equipment. Visual testing of printed circuit boards is used in the prior art to detect wiring pattern deviations, but such is unsatisfactory both in terms of cost and since some defects are difficult to detect visually and fatigue or physical condition of an inspector may affect test results. Accordingly, a completely reliable test method for locating short circuits and near short circuits has not been heretofore available.
Prior art attempts to mechanize testing of printed circuit wiring boards have been limited to spot checks of critical circuit locations or dynamic testing of circuit boards with connectors and/or components thereon, both of which materially increases the cost of locating defects and complicating any possible repairs. Even when defective patterns such as short circuits were located by mechanical or electrical tests, the location has not been identified specifically enough to facilitate repair and correction of the defect.
A further failure of prior art printed circuit board testers is complexity and unadaptability. If connectors need be affixed this makes the tests limited to known circuit pattern configurations and further is time consuming and awkward and introduces possibilities of errors in the connectors which are not usually made to withstand repeated connecting and disconnecting cycles over long periods of time.